Piezoelectric fans or blowers are available which use a piezoelectric bender attached at one end to a housing. A flexible blade is attached near or at the other, free end of the piezoelectric bender. When an alternating voltage is applied to the piezoelectric bender, the free end drives the flexible blade into oscillation and moves air or other fluid by generation and shedding of vortices from the tip of the blade, U.S. patent application, Ser. No. 477,630 filed Mar. 22, 1983, now U.S. Pat. No. 4,498,851. Such a device transmits vibrations to the housing. To reduce this vibration, the blowers are usually constructed with pairs of counter-oscillating piezoelectric benders and blades. This ordinarily eliminates vibration in the transverse mode due to the cancellation of momentum from the counter-oscillating benders and blades. However, since the blades perform arcuate oscillation, there are also momentum oscillations in the longitudinal direction which are not cancelled by the counter-oscillation in the transverse dimension. There results a longitudinal vibration of the housing, which can be absorbed if the blower is of substantially less mass than the housing, or if suitable damping can be provided. For larger blowers and where vibration causes problems, the longitudinal vibrations can be unacceptable. Employing a cancellation approach is not appropriate for a second counter-oscillating unit 180.degree. out of phase with the main unit, for unless the second unit could be designed to do useful work it would double the cost, mass, volume and components of the system without adding to its performance.